Sperm Quality in Young Bull Semen Can Be Improved by Single Layer Centrifugation.

Interest in using semen from young bulls is increasing due to identifying promising animals by genomic selection. However, sperm quality in these ejaculates may not reach currently accepted standards for the cattle breeding industry. The purpose of this study was to determine if centrifugation of semen from young bulls through the Bovicoll colloid could improve sperm quality sufficiently for the frozen semen to be acceptable for artificial insemination. Ejaculates from 19 young bulls were split and either processed by Single-Layer Centrifugation (SLC) or not (CON) before freezing. After thawing, sperm quality was evaluated by determination of membrane integrity, mitochondrial membrane potential, DNA integrity, production of reactive oxygen species, sperm morphology and motility. Approximately half of the CON samples reached acceptable post-thaw quality (membrane integrity ≥ 40%) despite being below the breeding company´s desired sperm concentration threshold pre-freezing. In the remaining samples, sperm quality was improved by SLC such that 45% of them reached acceptable quality post-thaw. Almost 75% of the young bull sperm samples could have produced usable frozen semen doses by adjusting the breeding company´s current processing protocols. Since lowering the generation interval has a direct effect on the genetic gain per year, SLC could aid genetic progress in cattle breeding.

Post-thaw semen quality in young bull ejaculates before being accepted for commercial semen doses.

BACKGROUND: Genomic selection enables bulls with desirable characteristics to be identified at a young age, but sperm quality can be poor in the ejaculates of young bulls. Few studies have been done on post-thaw sperm quality in bulls less than 10 months old. The objective of this study was to determine the age at which post-thaw sperm quality was acceptable for artificial insemination. METHODS: Semen was collected by artificial vagina; samples containing 100-500 million spermatozoa/ml were frozen for this study. Post-thaw analyses of membrane integrity (MI), mitochondrial membrane potential (MMP), chromatin integrity, morphology, production of reactive oxygen species and sperm kinematics were made. RESULTS: The age at which ejaculates exceeded the breeding company's thresholds of acceptance varied considerably among individuals, with 285 days being the earliest. Morphology (p < 0.003), MI (p = 0.0096), high MMP (p = 0.043) and superoxide production (p = 0.0084) increased between the first and last ejaculates but reached acceptable levels at different ages for individual bulls. CONCLUSIONS: It was possible to obtain acceptable post-thaw sperm quality from samples even though sperm concentration was lower than the breeding company's threshold. Therefore, it might be feasible to use ejaculates earlier than is currently considered possible, by modifying semen handling protocols.